To assess the safety, tolerability, and antiviral efficacy of ABT-378/Ritonavir at 200/100 mg bid, 400/100 mg bid, and 400/200 mg bid in combination with stavudine and lamivudine. Methods: Two groups of antiretroviral naive patients were enrolled and randomly assigned to a blinded ABT-378/ritonavir dose: Group I (200/100 mg or 400/100 mg bid); Group II (400/100 mg or 400/200 mg bid). During the first 14 days of treatment patients in Group I were required to either 1) come to the Duke GCRC twice a day to receive study medication, 2) come to the Duke GCRC once a day to receive first dose of study medication and then call in to the clinic after taking the second daily dose, or 3) receive study medication at home from a home health nurse. The purpose of the observed/monitored dosing was to educate patients on the importance of compliance and to ensure that doses were not missed. Group I patients were required to come to the Duke GCRC on study days 1, 4 or 5, 7, 9 or 10, and 14 for blood draws, vital signs, and electrocardiograms. After the first 14 days, study visits were planned for days 16, 21, and 28. Additional visits were scheduled once every two weeks until week 12 (month 3), once per month until month 6, and every three months thereafter. Group II patients were required to come to the Duke Infectious Disease Clinic every two weeks for the first month, once per month until month 6, and every three months thereafter. For both Group I and Group II patients, measurements of vital signs, physical examinations, and ECGs were repeated at study visits. Blood and urine samples were obtained for routine clinical laboratory evaluations, viral load, and CD4 and CD8 counts, and so that the levels of study drugs in the blood could be measured. All patients in Group I were required to stay in the GCRC on two occasions to participate in pharmacokinetic studies. None of the Group II patients were required to participate in any pharmacokinetic studies.